1. Field of the Invention
The present invention relates to a cylindrical vibration isolating device suitable for a sub-frame mount of motor vehicles.
2. Description of the Related Art
As an example of cylindrical vibration isolating devices in which an inner cylinder and an outer cylinder are connected by a vibration isolating rubber, there is known a sub-frame mount. This sub-frame mount is the cylindrical vibration isolating device having the inner and outer cylinders connected by the vibration isolating rubber, and has a large diameter portion formed of a vibration isolating rubber or the like on a partial surface of the outer cylinder. The large diameter portion is adapted to be press-fitted into a mounting hole of the sub-frame (as an example, see a patent reference 1).
Patent reference 1: Japanese patent laid-open publication No. 2004-211791.
FIG. 11 is a graph showing a change in a press fitting load when the sub-frame mount is press-fitted into the mounting hole provided in the sub-frame, wherein the vertical axis denotes the press fitting load and the horizontal axis denotes a press fitting stroke (a press fitting amount). A conventional sub-frame mount “a” shown in this graph is comprised of a flange “b” on one end thereof in the axial direction, a rubber seal “c” on the other end thereof, a large diameter portion “d” and a small diameter portion “e” on a middle barrel portion.
When this sub-frame mount “a” is press-fitted from the rubber seal portion “c” into the mounting hole of the sub-frame, firstly a comparatively small change of the press fitting load due to the change of the rubber seal portion “c” is created between a point P1 and a point P0. Next, when the large diameter portion “d” comes into contact with the mounting hole at the point P0, the press fitting load goes up rapidly to be a straight line of an acute angle between the point P0 and a point P4. This rapid rise of the press fitting load causes such a bad influence that the rubber seal portion “c” is damaged or that a crack is developed in a welded portion of the sub-frame.
Therefore, an object of the present invention is to prevent the rapid rise of the press fitting load.